1. Field of the Invention
The present invention relates to an insertion instrument which is provided with an insertion section extending along the longitudinal axis, and to an assistance tool which is attached to the insertion section of the insertion instrument and which rotates around the longitudinal axis when a driving force is transmitted.
2. Description of the Related Art
U.S. Patent Application Publication No. 2014/0330079 discloses a spiral unit (assistance tool) attached to the insertion section of an endoscope (insertion device). The spiral unit (a spiral tube and an outer rotatable cylinder) is detachably attached to the insertion section to cover the outer peripheral of the insertion section, and is provided with a spiral fin spirally extending, with the longitudinal axis of the insertion section as a center. In the insertion section, a rotatable cylinder (an inner rotatable cylinder) is attached to a base portion to be rotatable around the longitudinal axis. A plurality of rollers are attached to the rotatable cylinder, and the insertion section is provided with a projection projected by the rollers toward the outer peripheral side of the insertion section. In the state where the spiral unit is attached to the insertion section, a driving force is transmitted, and the rotatable cylinder and the rollers integrally rotate around the longitudinal axis. As a result, a pushing force acting around the longitudinal axis is applied from the projection of the insertion section to the proximal portion of the spiral unit. Accordingly, a driving force is transmitted to the spiral unit, and the spiral unit rotates around the longitudinal axis relative to the base portion. When the spiral unit rotates, with the spiral fin being pushed by the wall of a lumen or the like toward the inner peripheral side, a propulsion force acting toward the distal side or the proximal side is exerted on the spiral unit and the insertion section. According to U.S. Patent Application Publication No. 2014/0330079, a supporting surface which supports the spiral unit attached to the insertion section is provided on the outer peripheral surface of the insertion section (base portion) in a part on the proximal side with respect to the rotatable cylinder (projection). The inner peripheral surface of the spiral unit is provided with a sliding surface. In the state where the spiral unit attached to the insertion section rotates, the sliding surface slides on the supporting surface of the insertion section around the longitudinal axis.